1. Field of the Invention
The present invention relates to a roll sheet conveying apparatus which is used for a printer, a facsimile machine, a copying machine, and the like, and which draws out a sheet held in a roll and simultaneously conveys the sheet. More specifically, the present invention relates to a real-time motor control method for keeping constant the tension of a sheet to be conveyed even in a state in which a roll sheet is consumed gradually.
2. Description of the Related Art
In a roll sheet conveying apparatus for drawing out and conveying a sheet wound in a roll, it is desirable to apply certain tension between the roll sheet and a conveying roller for conveying the roll sheet in order to remove sheet curl and convey the roll sheet without slack or skew.
For example, Japanese Patent Laid-open No. 2009-242048 discloses measuring a load on a roll sheet by performing a preliminary identifying operation (System Identifying Performance) and applying appropriate tension according to a conveying speed. Further, Japanese Patent Laid-open No. H05-177084 (1993) discloses not a conveying apparatus, but a washing machine which preliminarily determines fabric capacity based on load torque obtained from a motor rotation speed and a duty ratio, and which supplies water in an amount suitable for the obtained fabric capacity.
However, the features disclosed in Japanese Patent Laid-open No. 2009-242048 and Japanese Patent Laid-open No. H05-177084 (1993) require an identifying operation for detecting the load on the roll sheet or the fabric capacity at timing different from that of an original operation and consume time and power for the identifying operation. Further, a friction load on the rotation of the roll sheet may vary depending on the remaining amount, type, lot, or use environment of the roll sheet, and drive control based on data obtained by performing the identifying operation does not necessarily function normally during the original operation. More specifically, in order to maintain appropriate tension irrespective of the type of the sheet, use environment the remaining amount of the roll sheet and the like, it is desirable to appropriately control a motor for rotating the roll sheet and the conveying roller during the original operation according to a change in these various conditions.